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TitleMicrostructural and fluid inclusion studies of orogenic gold deposits from the Red Lake and Abitibi greenstone belts, Canada: Implications for hydrodynamics and fluid-structural relationships
AuthorChi, G; Liu, Y; Bethume, K; Dubé, B; Guha, J
SourceGeological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Programs with Abstracts vol. 34, 2011 p. 39
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20130565
Meeting2011 GAC-MAC-SEG-SGA Joint Annual Meeting; Ottawa; CA; May 25-27, 2011
Mediapaper; on-line; digital
File formatpdf
Lat/Long WENS-94.0000 -93.5000 51.2500 51.0000
Subjectseconomic geology; structural geology; gold; mineralization; fluid inclusions; structural analyses; Red Lake Greenstone Belt; Abitibi Greenstone Belt; Campbell-Red Lake gold deposit
ProgramTargeted Geoscience Initiative (TGI-4), Gold Ore Systems
AbstractLarge fluid pressure fluctuations have been commonly documented in shear zone-related orogenic gold deposits, and interpreted to be largely responsible for opening and closing of fractures and associated fluid flow at a given stress condition, as outlined in the fault-valve model. However, combined microthermometric and microstructural studies of fluid inclusion planes (FIPs) from several localities in the Archean Red Lake greenstone belt and the Donalda gold deposit in the Abitibi greenstone belt appear to indicate that the local principal stresses may have flipped episodically during the formation of the auriferous quartz-carbonate veins. In the world-class Campbell-Red Lake gold deposit and smaller-scale deposits in the eastern Red Lake greenstone belt, a large number of carbonate ± quartz veins are developed along SEtrending subvertical deformation zones and are commonly parallel or subparallel to the foliation. Fluid inclusions in the pre-ore and syn-ore carbonate and quartz are dominantly carbonic, contrasting aqueous and aqueous-carbonic inclusions in post-ore minerals. Large fluid pressure ranges were estimated for the pre-ore (0.7- 3.5 Kb) and syn-ore (0.9-5.4 Kb) stages. Most of the FIPs are parallel or subparallel to the foliation. Although a reduced tensile strength along the foliation coupled with supralithostatic fluid pressure may explain the formation of the foliation-parallel veins with the ?1 being perpendicular to foliation and ?3 being subvertical, the orientation of the FIPs requires ?3 being subhorizontal, suggesting that ?3 may have flipped episodically during the incremental history of the veins. In the Donalda gold deposit in the southern Abitibi greenstone belt, two subhorizontal auriferous quartz veins are developed and slightly displaced by unmineralized subvertical shear zones. Fluid inclusions occurring in a randomly distributed mode and as intracrystal FIPs comprise aqueous and aqueous-carbonic types, whereas those in intercrystal FIPs representing post-ore fluids are only aqueous. FIPs and veinlets cutting primary vein minerals are mostly subvertical, indicating subhorizontal ?3. This local stress orientation is different from the regional stress field in which ?3 is subvertical, suggesting that the local stress field may have periodically changed in orientation during the growth of the vein. The episodic flipping of local principal stresses in shear zonerelated gold deposits, also reported elsewhere in the literature, may be related to episodic upwelling of deeply derived fluids and/or the bridging effect due to uneven mineral growth in fractures. Both factors are inherently associated the development of shear zonevein systems.